Fully Differential Rail-to-Rail Output Amplifier with Inverter-Based Input Pair

ABSTRACT

A fully differential rail-to-rail-output amplifier includes a differential input inverter pair, folded cascode pair, class AB control pair, and class AB output rail-to-rail pair. A drain associated with the folded cascode pair is operatively coupled to the class AB control pair, and the drain associated with the folded cascode pair is unconnected to the current source associated with the class AB control pair. A method of providing fully differential rail-to-rail-output amplification includes coupling a folded cascode pair operatively to a differential input inverter pair, coupling a drain associated with the folded cascode pair operatively to a class AB control pair, and coupling a class AB output rail-to-rail pair operatively to the class AB control pair.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of, and priority to, U.S. Provisional Application No. 62/872,945, filed Jul. 11, 2019, the disclosure of which is incorporated herein by reference in its entirety.

STATEMENT OF GOVERNMENT LICENSE RIGHTS

The present invention was made with government support under contract number DE-SC0012704 awarded by the U.S. Department of Energy. The United States government may have certain rights in this invention.

BACKGROUND

The disclosed embodiments generally relate to a circuit that reduces electronic noise associated with a fully differential amplifier.

SUMMARY

The disclosed embodiments relate to a fully differential rail-to-rail-output amplifier, which includes a differential input inverter pair, folded cascode pair, class AB control pair, and class AB output rail-to-rail pair. The differential input inverter pair includes at least one of a negative-channel or n-type channel metal-oxide semiconductor (NMOS) transistor, positive-channel or p-type channel metal-oxide semiconductor (PMOS) transistor, top current source, and/or bottom current source. The folded cascode pair includes at least one of a NMOS transistor and/or PMOS transistor. The folded cascode pair is operatively coupled to the differential input inverter pair. The class AB control pair includes at least one of a NMOS transistor, PMOS transistor, and/or current source. A drain associated with the folded cascode pair is operatively coupled to the class AB control pair, and the drain associated with the folded cascode pair is unconnected to the current source associated with the class AB control pair. The class AB output rail-to-rail pair includes at least one of a NMOS transistor and/or PMOS transistor, and the class AB output rail-to-rail pair is operatively coupled to the class AB control pair.

The fully differential rail-to-rail-output amplifier may include a top load current source operatively coupled to the folded cascode pair, and the top load current source may include at least one PMOS transistor. The fully differential rail-to-rail-output amplifier may include a bottom load current source operatively coupled to the folded cascode pair, and the bottom load current source may include at least one NMOS transistor.

The fully differential rail-to-rail-output amplifier may include a common mode feedback circuit operatively coupled to the top load current source, and the common mode feedback circuit may include at least one of a differential-input single-ended output amplifier and/or common mode detection circuit. The common mode feedback circuit may be operatively coupled to the bottom load current source, and the common mode feedback circuit may include at least one of a differential-input single-ended output amplifier and/or common mode detection circuit.

The differential input inverter pair may include at least two NMOS transistors and/or at least two PMOS transistors. Sources of the PMOS transistors associated with the differential input inverter pair may be operatively coupled to the top current source, and the top current source may be operatively coupled to a power supply. Sources of the NMOS transistors associated with the differential input inverter pair may be operatively coupled to the bottom current source, and the bottom current source may be operatively coupled to ground. Drains of the PMOS transistors associated with the differential input inverter pair and drains of the NMOS transistors associated with the differential input inverter pair may be operatively coupled to the folded cascode pair, and gates of at least one of the PMOS transistors associated with the differential input inverter pair and at least one of the NMOS transistors associated with the differential input inverter pair may be operatively coupled together.

The folded cascode pair may include at least two NMOS transistors, and sources of the NMOS transistors associated with the folded cascode pair may be operatively coupled to the differential input inverter pair. At least one drain of the NMOS transistors associated with the folded cascode pair may be operatively coupled to the class AB control pair. The folded cascode pair may include at least two PMOS transistors, and sources of the PMOS transistors associated with the folded cascode pair may be operatively coupled to the differential input inverter pair. At least one drain of the PMOS transistors associated with the folded cascode pair may be operatively coupled to the class AB control pair.

A source of the PMOS transistor associated with the class AB control pair and a drain of the NMOS transistor associated with the class AB control pair may be operatively coupled to the folded cascode pair, and a drain of the PMOS transistor associated with the class AB control pair and a source of the NMOS transistor associated with the class AB control pair may be operatively coupled to the current source associated with the AB control pair. The current source associated with the class AB control pair may be operatively coupled to ground. A source of the PMOS transistor associated with the class AB control pair and a drain of the NMOS transistor associated with the class AB control pair may be operatively coupled to the folded cascode pair, and a drain of the PMOS transistor associated with the class AB control pair and a source of the NMOS transistor associated with the class AB control pair may be operatively coupled to the current source associated with the AB control pair. The current source associated with the class AB control pair may be operatively coupled to a power supply.

A drain of the PMOS transistor associated with the class AB output rail-to-rail pair may be operatively coupled to a drain of the NMOS transistor associated with the class AB output rail-to-rail pair, and a gate of the PMOS transistor associated with the class AB output rail-to-rail pair may be operatively coupled to the class AB control pair. A gate of the NMOS transistor associated with the class AB output rail-to-rail pair may be operatively coupled to the class AB control pair.

The top load current source may include at least two PMOS transistors, and gates of the PMOS transistors associated with the top load current source may be operatively coupled together. Sources of the PMOS transistors associated with the top load current source may be operatively coupled to a power supply, and drains of the PMOS transistors associated with the top load current source may be operatively coupled to the folded cascode pair. The bottom load current source may include at least two NMOS transistors, and gates of the NMOS transistors associated with the bottom load current source may be operatively coupled together. Sources of the NMOS transistors associated with the top load current source may be operatively coupled to ground, and drains of the NMOS transistors associated with the top load current source may be operatively coupled to the folded cascode pair.

The common mode detection circuit may be operatively coupled to drains of the PMOS transistor and the NMOS transistor associated with the class AB output rail-to-rail pair and the differential-input single-ended output amplifier, and the differential-input single-ended output amplifier may be operatively coupled to the top load current source and a direct current (DC) common mode voltage V_(CM). The common mode detection circuit may be operatively coupled to drains of the PMOS transistor and NMOS transistor associated with the class AB output rail-to-rail pair and the differential-input single-ended output amplifier, and the differential-input single-ended output amplifier may be operatively coupled to the bottom load current source and a direct current (DC) common mode voltage V_(CM).

The disclosed embodiments further relate to a method of providing fully differential rail-to-rail-output amplification, which includes coupling a folded cascode pair operatively to a differential input inverter pair, coupling a drain associated with the folded cascode pair operatively to a class AB control pair, and coupling a class AB output rail-to-rail pair operatively to the class AB control pair. The folded cascode pair includes at least one of a NMOS transistor and/or PMOS transistor. The differential input inverter pair includes at least one of a NMOS transistor, PMOS transistor, top current source, and/or bottom current source. A drain associated with the folded cascode pair is unconnected to a current source associated with the class AB control pair, and the class AB control pair includes at least one of a NMOS transistor, PMOS transistor, and/or current source. The class AB output rail-to-rail pair includes at least one of a NMOS transistor and/or PMOS transistor.

Other embodiments will become apparent from the following detailed description considered in conjunction with the accompanying drawings. It is to be understood, however, that the drawings are designed as an illustration only and not as a definition of the limits of any of the embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a two-stage fully differential rail-to-rail-output amplifier with differential input inverter pairs, folded cascode pair, and class AB control pairs in a first amplifying stage, followed by a class AB output rail-to-rail stage, wherein the folded cascode pair is realized with NMOS-type transistors; and

FIG. 2 is a block diagram of an embodiment of the two-stage fully differential rail-to-rail-output amplifier shown in FIG. 1, in which the folded cascode pair is realized with PMOS-type transistors;

FIG. 3 is a block diagram of an embodiment of a fully differential amplifier with inverter-based input pairs;

FIG. 4 is a block diagram of an embodiment of a fully differential rail-to-rail-output amplifier with the inverter-based input pairs, in which class AB control pairs are biased by a separate current source, thereby providing substantially greater voltage headroom for the folded cascode pair; and

FIG. 5 is a block diagram of an embodiment of a fully differential rail-to-rail-output amplifier with the inverter-based input pairs, in which noise from a bottom bias current source is cancelled and noise from parasitic resistors R_(S) is reduced by greater than the square root of 2 (sqrt(2)).

DETAILED DESCRIPTION

Electronic noise is a factor in limiting the resolution of an electronic system. Fully differential amplifiers are used in medical imagers, particle detectors, biomedical circuits, and other technologies. To reduce the noise of the electronic system, techniques may require a substantial increase in power consumption. However, some applications have a limit on power consumption and, as a result, a limit on resolution of the electronic system. Accordingly, a circuit that can reduce electronic noise, increase bandwidth associated with fully differential amplifiers, and/or reduce power consumption, while maintaining a specified level of resolution and/or performance would be highly beneficial.

Embodiments of a circuit architecture are described herein that are capable of reducing electronic noise associated with fully differential amplifiers by at least 3 dB, while maintaining the same and/or similar power consumption, thereby enabling resolution associated with the fully differential amplifier to be increased by at least 3 dB.

FIG. 1 shows a block diagram of a two-stage fully differential rail-to-rail-output amplifier 10 including a folded cascode pair 12 a-b, differential input inverter pairs 14 a-d, and class AB control pairs 16 a-f in a first amplifying stage, followed by class AB output rail-to-rail pairs 18 a-c, in which the folded cascode pair 12 a-b is realized with NMOS technology.

As used herein, the first stage of the subject architecture includes transistors M0 14 a-b, M1 14 c-d, M2 12 a-b, M3 20 a-b, M4 16 a-b, M5 16 c-d, and current sources I_(ABa) 16 e, I_(ABb) 16 f. In other words, the first stage includes the input pairs (transistors M0 a 14 a, M1 a 14 c, M0 b 14 b, M1 b 14 d), folded cascode pair (transistors M2 a 12 a, M2 b 12 b), a top load current source (transistors M3 a 20 a, M3 b 20 b), a class AB control pairs (transistors M4 a 16 a, M5 a 16 c, M4 b 16 b, M5 b 16 d), and input pair biasing current sources I_(ABa) 16 e, I_(ABb) 16 f. As used herein, a second stage of the subject architecture includes transistors M6 18 a-b, M7 18 c-d. That is, the second stage includes the class AB output rail-to-rail pair (transistors M6 a 18 a, M7 a 18 c, M6 b 18 b, M7 b 18 d).

The input pairs 14 a-d include one pair of transistors that is designated as, for example, M0 a 14 a and M1 a 14 c, and another pair of transistors that is designated as, for example, M0 b 14 b and M1 b 14 d. The folded-cascade pair 12 a-b directs current to a specified pair of transistors, which is designated as, for example, M2 a 12 a and M2 b 12 b. The class AB control pairs are used for one class AB control, which is designated as, for example, M4 a 16 a and M5 a 16 c, and another class AB control, which is designated as, for example, M4 b 16 b and M5 b 16 d. One of the class AB control pairs, such as M4 a 16 a and M5 a 16 c, includes node V_(xa) 22, and the other class AB control pair, such as M4 b 16 b and M5 b 16 d, includes node V_(xb) 24. The subject circuit includes a modification to the class AB control pairs 16 a-f, in which (i) nodes V_(xa) 22, V_(xb) 24 and drains of the folded cascode pair M2 a 12 a or M2 b 12 b are disconnected or unconnected, which are then able to operatively coupled to one or more external circuits that generate an appropriate bias voltage using techniques known in the art, (ii) current sources I_(ABa) 16 e, I_(ABb) 16 f are added to the circuit, and nodes V_(xa) 22, V_(xb) 24 and current sources I_(ABa) 16 e, I_(ABb) 16 f are connected to the same ground, and (iii) drains of the folded cascode pair M2 a 12 a, M2 b 12 b are connected to the top load current source M3 a 20 a, M3 b 20 b, as shown in FIG. 1. A voltage VDD is a power supply, V_(IP) 26 is a positive input voltage, V_(IN) 28 is a negative input voltage, V_(OP) 30 is a positive output voltage, and V_(ON) 32 is a negative output voltage.

Embodiments of the subject fully differential output rail-to-rail amplifier 10 disclosed herein include a combination of the differential input inverter pairs (or input pairs) 14 a-d, folded-cascode pair 12 a-b, class AB control pairs 16 a-f, and class AB output rail-to-rail pairs 18 a-d. In addition, the subject amplifier comprises current sources 16 e-f, 14 e-f, and 20 a-b biasing the circuit, as well as a common mode feedback circuit 34 a-b.

The common mode feedback circuit 34 a-b includes a common-mode detection or common-mode sensing circuit 34 b that can be implemented using a variety of techniques know in the art. For example, in one embodiment, the common-mode sensing circuit 34 b is implemented using a set of two (2) capacitors and two (2) resistors electrically coupled in parallel. The common mode feedback circuit 34 a-b also includes a differential-input single-ended output amplifier 34 a. The differential-input single-ended output amplifier 34 a can also be implemented using a variety of techniques known in the art. For example, in one embodiment, the differential-input single-ended output amplifier 34 a is implemented using a set of three (3) NMOS and two (2) PMOS transistors.

The first stage of the subject amplifier 10 includes the differential inverter input pairs 14 a-d, folded cascode pair 12 a-b, class AB control pairs 16 a-f, and top load current source 20 a-b that biases the class AB control pairs 16 a-f.

The differential inverter input pairs 14 a-d include a set of PMOS transistors 14 a-b and a set of NMOS transistors 14 c-d generating signal currents upon application of a differential stimuli to the amplifier's input terminals 26, 28. The differential inverter input pairs 14 a-d are coupled to the amplifier's positive and negative inputs 26, 28, top and bottom bias current sources 14 e-f, and sources of the folded-cascode pair 12 a-b.

A top bias current source 14 e biases the differential inverter input pairs 14 a-d. The top bias current source 14 e is coupled between a power supply VDD and sources of the PMOS transistors 14 a-b.

A bottom bias current source 14 f biases the differential inverter input pair 14 a-d and folded-cascode pair 12 a-b. The bottom bias current source 14 f is coupled between sources of the NMOS transistors 14 c-d and ground.

The folded-cascode pair 12 a-b provides a low impedance path for the signal current. The folded-cascode pair 12 a-b is coupled to drains of the differential inverter input pairs 14 a-d, inputs of the class AB control pairs 16 a-f, and the top load current source 20 a-b.

The top load current source 20 a-b (i) converts signal currents generated in the differential inverter input pairs 14 a-d to voltages at nodes V_(Ya) 36, V_(Yb 38), (ii) supplies DC bias currents to the folded-cascode pair 12 a-b, the class AB control pairs 16 a-f, and the differential inverter input pairs 14 a-d, and (iii) provides a common-mode feedback path to the first stage of the amplifier 10. The top load current-source 20 a-b is coupled to the folded-cascode pair 12 a-b, class AB control pairs 16 a-f, and power supply VDD.

The class AB control pairs 16 a-f replicate voltages at nodes V_(Ya) 36 and V_(Yb) 38 to voltages at nodes V_(xa) 22 and V_(xb) 24, respectively. Signal currents generated in the differential inverter input pairs 14 a-d is converted to a voltage by a current source at nodes V_(Ya) 36 and V_(Yb) 38. For example, current that flows through the folded-cascode pair 12 a-b is converted to a voltage at V_(Ya) 36 and replicated to V_(xa) 22. This conversion ensures that when V_(Ya) 36 changes, V_(xa) 22 follows this change.

The class AB control pairs 16 a-d are biased using current sources I_(ABa) 16 e, I_(ABb) 16 f, and is coupled to the top load current source 20 a-b, drains of the folded-cascode pair 12 a-b, and input terminals of the class AB output pairs 16 a-f.

The class AB output pairs 18 a-d provide class AB and output-rail-to-rail capability. The class AB output pairs 18 a-d include input terminals coupled to terminals of the class AB control pairs 16 a-f. Drains of the class AB output pairs 18 a-d provide outputs of the fully differential amplifier 10 at output nodes 30, 32.

The subject amplifier 10 includes a common mode feedback loop 34 a-b. The common mode feedback loop 34 a-b senses a common mode voltage at the output nodes 30, 32. The common mode voltage is compared with a predetermined direct current (DC) common mode voltage V_(CM) 40 to determine an error signal 46. The error signal 46 is fed back to the first amplifier stage through the top load current source 20 a-b.

In the architecture of the fully differential amplifier 10 with the folded-cascode pair 12 a-b following the differential input pairs 14 a-d, the noise performance is defined by the transconductance of a pair of single input transistors. Increasing the current flowing through the transistors, increases the transconductance, and decreases the amplifier noise. The transconductance is proportional to the current flowing through the transistor. In the subject architecture, almost all of the power is dissipated in the first stage of the amplifier, which includes the input pairs 14 a-d, folded cascode pair 12 a-b, and class AB control pairs 16 a-f, which contributes to the transconductance of the input pairs 14 a-d. As a result, power resolution as a product, is advantageously reduced. Further, in low supply voltage applications, the current sources 14 e-f, 20 a-b that bias the folded cascode pair 12 a-b and the input pairs 14 a-d contributes to a level of noise comparable with the input pair of transistors.

In some embodiments, rather than two (2) transistors (e.g., PMOS) in the input pairs 14 a-d, four (4) transistors are utilized, i.e., a series combination of NMOS and PMOS transistors, which is also referred to as an inverter. The inverter may be added by itself without any other modification as shown in FIG. 3, or added in combination with additional modifications discussed herein as shown in FIGS. 1, 2, 4, and 5.

In FIG. 1., the fully differential rail-to-rail-output amplifier 10 is shown with the input pairs 14 a-d and modifications to the input pairs (M0 a 14 a, M1 a 14 c, M0 b 14 b, M1 b 14 d). The class AB control pairs 16 a-f are biased by one or more current source I_(TI) 14 e, I_(BI) 14 f separate from the current source biasing the input pair 14 a-d, thereby increasing voltage headroom available for the folded cascode pair M2 a 12 a, M2 b 12 b.

In some embodiments, the subject amplifier 10 may alternatively be realized using PMOS devices in the input inverter pairs. The current source I_(TI) is then connected between PMOS source terminals and the power supply VDD. Thus, the current source I_(TI) biases the input pairs in these embodiments.

The input pairs include PMOS transistors 14 a-b forming a PMOS differential pair. The PMOS transistors 14 a-b are coupled to the power supply VDD through the top current source I_(TI) 14 e. The input pairs 14 a-d also include NMOS transistors 14 c-d. The PMOS transistors 14 a-b are coupled to the NMOS transistors 14 c-d through nodes V_(Da) 42, V_(Db) 44. The NMOS transistors 14 c-d operate as a current sink and/or a current mirror load for the input pairs 14 a-d. The PMOS transistors 14 c-d may also be biased by a bias voltage.

The input pairs 14 a-d drive output signals using, for example, current to the folded cascode pair M2 a 12 a, M2 b 12 b. The folded-cascode pair M2 a 12 a, M2 b 12 b provides a low impedance path for the output signal of the input pairs 14 a-d. The folded cascode pair M2 a 12 a, M2 b 12 b is coupled to drains of the input pairs 14 a-d, input of the class AB control pairs 16 a-f, and top load current source M3 a 20, M3 b 20 b.

The top load current source M3 a 20 a, M3 b 20 b is connected between drains of the folded-cascode pair M2 a 12 a, M2 b 12 b and the power supply VDD. The top load current source M3 a 20 a, M3 b 20 b converts signal currents generated in the differential inverter input pairs 14 a-d to voltages at nodes V_(ya) 36, V_(yb) 38. To a first order approximation, signal current generated by the input pairs 14 a-d is converted to voltage at nodes V_(ya) 36, V_(yb) 38 by the output impedance of the first stage load current source. However, if the input impedances of the class AB control pairs 16 a-f are of the same order as the output impedance of the top load current source M3 a 20 a, M3 b 20 b, a parallel combination of these impedances converts the signal current to voltages at nodes V_(ya) 36, V_(yb) 38.

The folded cascode pair 12 a-b, input pairs M0 14 a-b, M1 14 c-d, and/or class AB control pairs 16 a-f form, in part, a folded cascode amplifier. For example, the folded cascode pair 12 a-b may be “folded” about nodes as known in the art. The concept of cascode transistors is used to increase amplifier output impedance and provide a low-impedance path for current generated by input transistors to the output stage. As a result, this technique boosts the amplifier gain. In the subject architecture, a standard cascode transistor approach is replaced by a folded cascode technique, which provides a low-impedance path for the current generated by input transistors to the output nodes V_(ya) 36, V_(yb) 38 of the first amplifier stage. The folded cascode technique also increases first stage output impedance and de-desensitizes the input pair 14 a-d from the effect of voltage variations to the output nodes V_(ya) 36, V_(yb) 38. The gates of the folded cascode are biased by voltage generated in accordance with techniques known in the art.

The NMOS transistors 12 a-b may be configured as common-gate transistors. In some embodiments, gates of the NMOS transistors 12 a-b may be biased by a voltage source. The NMOS transistors 12 a-b provide voltages at nodes Vd0 and Vd1 as shown in FIG. 3 based on the dimensions of the transistors used, threshold voltage, current flowing through the drain and source of the folded cascode pair 12 a-b, and/or bias voltage at the gates of the folded cascode pair 12 a-b. The bias and cascode voltages may be generated in accordance with methods known in the art.

A biasing circuit may be configured to bias the cascode pair 12 a-b with or without relying on external reference signals using techniques known in the art. For example, in some embodiments, the biasing circuit may include resistors and/or transistors. The resistors may be configured as a voltage divider configuration sourcing voltage from the power supply VDD. The resistors may further be coupled to gates of the folded-cascode pair 12 a-b.

The top load current source 20 a-b is connected to the common mode feedback circuit 34 a-b. In some embodiments, the common mode feedback circuit or loop 34 a-b is coupled to output signals V_(OP) 30, V_(ON) 32 to generate a common mode voltage of the output signal. Output transistors apply voltage to each output and, as a result, the current and gain of the corresponding output may be doubled. In some embodiments, the class AB control pair 16 a-f generates output signals V_(OP) 30, V_(ON) 32.

The common mode feedback loop 34 a-b senses the common mode voltage at the output nodes V_(OP) 30, V_(ON) 32. The common mode voltage is compared with a predetermined and/or desired DC voltage V_(CM) 40 to determine an error signal. The error signal 46 is fed back to the first amplifier stage that comprises the input inverter pairs 14 a-d, folded cascode pair 12 a-b, and class AB control pairs 16 a-f. The error signal 46 can be applied to the top current source I_(TI) 14 e or bottom current source I_(BI) 14 f in the input stage to bias current sources I_(Aba) 16 e, I_(ABb) 16 f of the class AB control pairs 16 a-f.

The subject amplifier 10 may at least double the transconductance of the input pairs 14 a-d and direct all or substantially all of the current flowing from the first stage of the input branch, and thus substantially less or no current is wasted. Further, the subject amplifier 10 removes noise contributions from current sources I_(BI), I_(BT) shown in FIGS. 1-5. In addition, the subject amplifier 10 decreases the noise contribution from parasitic source resistors R_(S) 56 shown in FIG. 5 by at least 3 dB (or a factor of two). These improvements yield a 3 dB (or factor of two) improvement in noise reduction for the system. Thus, the subject amplifier exhibits a 3 dB (or factor of two) improvement over conventional approaches.

A method for providing the subject circuit includes 1) disconnecting Vx (now V_(xa) 22, V_(xb) 24) and the drain of folded cascode pair (now M2 a 12 a, M2 b 12 b) from each other; 2) coupling Vx (now V_(xa) 22, V_(xb) 24) to a current source 16 e, 16 f connected to ground; and 3) connecting drains of the folded cascode pair (now M2 a 12 a, M2 b 12 b) to Vy (now V_(ya) 36, V_(yb) 38). The subject circuit modifies the Class AB control pairs 16 a-f in a fully differential rail-to-rail output amplifier with inverter-based input pairs of transistors 14 a-d. This modification includes disconnecting Vx 22, 24 from the current source and drains of the folded cascode pair M2 12 a-b, and moving drains of the folded cascode pair M2 12 a-b connection to the current source Vy (now V_(ya) 36, V_(yb) 38).

In summary, the subject circuit 10 includes input pairs 14 a-d, folded cascode pair 12 a-b, class AB control pairs 16 a-f, and common mode feedback loop 34 a-b. The class AB control pairs 16 a-f further include voltage nodes V_(xa) 22, V_(ya) 36, V_(xb) 24, V_(yb).38. The input pairs 14 a-d are configured to receive an input signal, process the input signal, and provide an input stage output signal to the class AB control pairs 16 a-f. In one embodiment, the input pairs 14 a-d generate an input stage output signal based on a transconductance associated with the input pairs 14 a-d. The input pairs 14 a-d process the input signal and provides an input stage output signal to the folded cascode pair 12 a-b or the class AB control pairs 16 a-d.

The folded cascode pair M2 a 12 a, M2 b 12 b generates a folded cascode pair output signal based on the input pair output signal. In one embodiment, the folded cascode pair 12 a-b includes a pair of inverters. Each inverter include a pair of transistors 12 a-b. In some embodiments, the folded cascode pair 12 a-b generates a folded cascode pair output signal based on a voltage gain having, for example, a gain factor determined by a ratio of the folded cascode pair output signal to the input pair output signal. The conversion of current to voltage is provided by the folded cascode pair 12 a-b.

The subject amplifier 10 includes the fully differential voltage amplifier, characterized by the differential inputs 26, 28 and differential outputs 30, 32. As used herein, the fully differential voltage amplifier includes an output controlled by two feedback paths 30, 32 that, because of the amplifier's high gain, determine the output voltage for any given input. Common-mode noise, such as power supply disturbances are rejected, which renders fully differential amplifiers desirable as part of a mixed-signal integrated circuit.

FIG. 2 is a block diagram of another embodiment of the two-stage fully differential rail-to-rail-output amplifier 50 shown in FIG. 1, in which the folded cascode pair 12 c-d is implemented using PMOS transistors 12 c-d. Additional distinctions between the embodiment 10 shown in FIG. 1 and the embodiment 50 shown in FIG. 2 include biasing the class AB control pairs 16 a-d using current sources I_(ABa) 16 e, I_(ABb) 16 f, which are coupled between the AB control pair transistors 16 a-d and VDD, and coupling the class AB control pairs 16 a-d to a bottom load current source 20 c-d, which is implemented using NMOS transistors 20 c-d. In addition, the bottom load current source 20 c-d is coupled to the common mode feedback circuit 34 a-b.

FIG. 3 shows a block diagram of an embodiment of the fully differential amplifier, in which only the inverter-based input pairs 14 a-d have been implemented. FIG. 4 shows a block diagram of an embodiment of the fully differential rail-to-rail-output amplifier including the inverter-based input pairs 14 a-d, in which the class AB control pairs 16 a-d are biased using separate current sources 16 e-f, thereby providing substantially greater voltage headroom for the folded cascode pair 16 a-f. FIG. 5 shows a block diagram of an embodiment of the fully differential rail-to-rail-output amplifier including the inverter-based input pair 14 a-d, in which noise from the bottom bias current source 14 f is cancelled and noise from parasitic resistors R_(S) 56 is reduced by greater than the square root of 2 (sqrt(2)).

It is recognized that any technically feasible combination of input pairs and folded cascode pair may be used to receive the input signal and generate the output signal. All publications and patents mentioned in the above specification are incorporated by reference in this specification. Various modifications and variations of the described detector(s) and its components will be apparent to those skilled in the art without departing from the scope and spirit of the invention. Although the disclosure has been described in connection with specific preferred embodiments, it should be understood that the invention as claimed should not be unduly limited to such specific embodiments. Indeed, those skilled in the art will recognize, or be able to ascertain using no more than routine experimentation, many equivalents to the specific embodiments of the invention described herein. Such equivalents are intended to be encompassed by the following claims.

Although the specification describes components and functions implemented in the embodiments with reference to particular standards and protocols, the embodiments are not limited to such standards and protocols.

The illustrations of embodiments described herein are intended to provide a general understanding of the structure of various embodiments, and they are not intended to serve as a complete description of all the elements and features of apparatus and systems that might make use of the structures described herein. Many other embodiments will be apparent to those of skill in the art upon reviewing the above description. Other embodiments are utilized and derived therefrom, such that structural and logical substitutions and changes are made without departing from the scope of this disclosure. Figures are also merely representational and are not drawn to scale. Certain proportions thereof are exaggerated, while others are decreased. Accordingly, the specification and drawings are to be regarded in an illustrative rather than a restrictive sense.

Embodiments are referred to herein, individually and/or collectively, by the term “embodiment” merely for convenience and without intending to voluntarily limit the scope of this application to any single embodiment or inventive concept if more than one is in fact shown. Thus, although specific embodiments have been illustrated and described herein, it should be appreciated that any arrangement calculated to achieve the same purpose are substituted for the specific embodiments shown. This disclosure is intended to cover any and all adaptations or variations of various embodiments. Combinations of the above embodiments, and other embodiments not specifically described herein, will be apparent to those of skill in the art upon reviewing the above description.

The abstract is provided to comply with 37 C.F.R. § 1.72(b), which requires an abstract that will allow the reader to quickly ascertain the nature of the technical disclosure. It is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims. In addition, in the foregoing Detailed Description, it can be seen that various features are grouped together in a single embodiment for the purpose of streamlining the disclosure. This method of disclosure is not to be interpreted as reflecting an intention that the claimed embodiments require more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive subject matter lies in less than all features of a single embodiment. Thus, the following claims are hereby incorporated into the detailed description, with each claim standing on its own as separately claimed subject matter.

Although specific example embodiments have been described, it will be evident that various modifications and changes are made to these embodiments without departing from the broader scope of the inventive subject matter described herein. Accordingly, the specification and drawings are to be regarded in an illustrative rather than a restrictive sense. The accompanying drawings that form a part hereof, show by way of illustration, and without limitation, specific embodiments in which the subject matter are practiced. The embodiments illustrated are described in sufficient detail to enable those skilled in the art to practice the teachings herein. Other embodiments are utilized and derived therefrom, such that structural and logical substitutions and changes are made without departing from the scope of this disclosure. This detailed description, therefore, is not to be taken in a limiting sense, and the scope of various embodiments is defined only by the appended claims, along with the full range of equivalents to which such claims are entitled.

Given the teachings provided herein, one of ordinary skill in the art will be able to contemplate other implementations and applications of the techniques of the disclosed embodiments. Although illustrative embodiments have been described herein with reference to the accompanying drawings, it is to be understood that these embodiments are not limited to the disclosed embodiments, and that various other changes and modifications are made therein by one skilled in the art without departing from the scope of the appended claims. 

What is claimed is:
 1. A fully differential rail-to-rail-output amplifier, which comprises: a differential input inverter pair, the differential input inverter pair comprising at least one of an n-type channel metal-oxide semiconductor (NMOS) transistor, p-type channel metal-oxide semiconductor (PMOS) transistor, top current source, bottom current source; a folded cascode pair, the folded cascode pair comprising at least one of a NMOS transistor, PMOS transistor, the folded cascode pair operatively coupled to the differential input inverter pair; a class AB control pair, the class AB control pair comprising at least one of a NMOS transistor, PMOS transistor, current source, a drain associated with the folded cascode pair operatively coupled to the class AB control pair, the drain associated with the folded cascode pair being unconnected to the current source associated with the class AB control pair; and a class AB output rail-to-rail pair, the class AB output rail-to-rail pair comprising at least one of a NMOS transistor, PMOS transistor, the class AB output rail-to-rail pair operatively coupled to the class AB control pair.
 2. The fully differential rail-to-rail-output amplifier, as defined by claim 1, further comprising a top load current source, the top load current source operatively coupled to the folded cascode pair.
 3. The fully differential rail-to-rail-output amplifier, as defined by claim 2, wherein the top load current source comprises at least one PMOS transistor.
 4. The fully differential rail-to-rail-output amplifier, as defined by claim 1, further comprising a bottom load current source, the bottom load current source operatively coupled to the folded cascode pair.
 5. The fully differential rail-to-rail-output amplifier, as defined by claim 4, wherein the bottom load current source comprises at least one NMOS transistor.
 6. The fully differential rail-to-rail-output amplifier, as defined by claim 2, further comprising a common mode feedback circuit, the common mode feedback circuit operatively coupled to the top load current source.
 7. The fully differential rail-to-rail-output amplifier, as defined by claim 6, wherein the common mode feedback circuit comprises at least one of a differential-input single-ended output amplifier, common mode detection circuit.
 8. The fully differential rail-to-rail-output amplifier, as defined by claim 4, further comprising a common mode feedback circuit, the common mode feedback circuit operatively coupled to the bottom load current source.
 9. The fully differential rail-to-rail-output amplifier, as defined by claim 8, wherein the common mode feedback circuit comprises at least one of a differential-input single-ended output amplifier, common mode detection circuit.
 10. The fully differential rail-to-rail-output amplifier, as defined by claim 1, wherein the differential input inverter pair comprises at least two NMOS transistors, at least two PMOS transistors, sources of the PMOS transistors associated with the differential input inverter pair operatively coupled to the top current source, the top current source operatively coupled to a power supply, sources of the NMOS transistors associated with the differential input inverter pair operatively coupled to the bottom current source, the bottom current source operatively coupled to ground, drains of the PMOS transistors associated with the differential input inverter pair and drains of the NMOS transistors associated with the differential input inverter pair operatively coupled to the folded cascode pair, gates of at least one of the PMOS transistors associated with the differential input inverter pair and at least one of the NMOS transistors associated with the differential input inverter pair operatively coupled together.
 11. The fully differential rail-to-rail-output amplifier, as defined by claim 1, wherein the folded cascode pair comprises at least two NMOS transistors, sources of the NMOS transistors associated with the folded cascode pair operatively coupled to the differential input inverter pair, at least one drain of the NMOS transistors associated with the folded cascode pair operatively coupled to the class AB control pair.
 12. The fully differential rail-to-rail-output amplifier, as defined by claim 1, wherein the folded cascode pair comprises at least two PMOS transistors, sources of the PMOS transistors associated with the folded cascode pair operatively coupled to the differential input inverter pair, at least one drain of the PMOS transistors associated with the folded cascode pair operatively coupled to the class AB control pair.
 13. The fully differential rail-to-rail-output amplifier, as defined by claim 1, wherein a source of the PMOS transistor associated with the class AB control pair and a drain of the NMOS transistor associated with the class AB control pair are operatively coupled to the folded cascode pair, a drain of the PMOS transistor associated with the class AB control pair and a source of the NMOS transistor associated with the class AB control pair operatively coupled to the current source associated with the AB control pair, the current source associated with the class AB control pair operatively coupled to ground.
 14. The fully differential rail-to-rail-output amplifier, as defined by claim 1, wherein a source of the PMOS transistor associated with the class AB control pair and a drain of the NMOS transistor associated with the class AB control pair are operatively coupled to the folded cascode pair, a drain of the PMOS transistor associated with the class AB control pair and a source of the NMOS transistor associated with the class AB control pair operatively coupled to the current source associated with the AB control pair, the current source associated with the class AB control pair operatively coupled to a power supply.
 15. The fully differential rail-to-rail-output amplifier, as defined by claim 1, wherein a drain of the PMOS transistor associated with the class AB output rail-to-rail pair is operatively coupled to a drain of the NMOS transistor associated with the class AB output rail-to-rail pair, a gate of the PMOS transistor associated with the class AB output rail-to-rail pair operatively coupled to the class AB control pair, a gate of the NMOS transistor associated with the class AB output rail-to-rail pair operatively coupled to the class AB control pair.
 16. The fully differential rail-to-rail-output amplifier, as defined by claim 2, wherein the top load current source comprises at least two PMOS transistors, gates of the PMOS transistors associated with the top load current source operatively coupled together, sources of the PMOS transistors associated with the top load current source operatively coupled to a power supply, drains of the PMOS transistors associated with the top load current source operatively coupled to the folded cascode pair.
 17. The fully differential rail-to-rail-output amplifier, as defined by claim 4, wherein the bottom load current source comprises at least two NMOS transistors, gates of the NMOS transistors associated with the bottom load current source operatively coupled together, sources of the NMOS transistors associated with the top load current source operatively coupled to ground, drains of the NMOS transistors associated with the top load current source operatively coupled to the folded cascode pair.
 18. The fully differential rail-to-rail-output amplifier, as defined by claim 7, wherein the common mode detection circuit is operatively coupled to drains of the PMOS transistor and the NMOS transistor associated with the class AB output rail-to-rail pair and the differential-input single-ended output amplifier, the differential-input single-ended output amplifier operatively coupled to the top load current source and a direct current (DC) common mode voltage V_(CM).
 19. The fully differential rail-to-rail-output amplifier, as defined by claim 9, wherein the common mode detection circuit is operatively coupled to drains of the PMOS transistor and NMOS transistor associated with the class AB output rail-to-rail pair and the differential-input single-ended output amplifier, the differential-input single-ended output amplifier operatively coupled to the bottom load current source and a direct current (DC) common mode voltage V_(CM).
 20. A method of providing fully differential rail-to-rail-output amplification, which comprises: coupling a folded cascode pair operatively to a differential input inverter pair, the folded cascode pair comprising at least one of a n-type channel metal oxide semiconductor (NMOS) transistor, p-type channel metal oxide semiconductor (PMOS) transistor, the differential input inverter pair comprising at least one of a NMOS transistor, PMOS transistor, top current source, bottom current source; coupling a drain associated with the folded cascode pair operatively to a class AB control pair, the drain associated with the folded cascode pair being unconnected to a current source associated with the class AB control pair, the class AB control pair comprising at least one of a NMOS transistor, PMOS transistor, current source; and coupling a class AB output rail-to-rail pair operatively to the class AB control pair, the class AB output rail-to-rail pair comprising at least one of a NMOS transistor, PMOS transistor. 